The present invention relates to a rotor for an axial-flow type machine such as an axial compressor for industrial use, axial compressor of a gas turbine, steam turbine or the like and, more particularly, to a stacked rotor wherein a plurality of discs, each having radial rotor blades on its outer periphery, are stacked axially and joined to each other by stacking bolts.
Since that rotor blades of axial-flow type machines such as, for example, an axial compressor, are often damaged due to the drawing in of foreign matters or the like, the use of stacked rotor, composed of a plurality of discs axially stacked and joined to form one body, is quite advantageous in that the stacked rotor enables an easy removal and replacement of rotor blades on the outer periphery of the rotor. Additionally, the stacked rotor affords a reduction in weight of the rotor through a reduction in weight of each disc. The reduced weight of the rotor reduces the inertia of the rotor which, in turn, permits a reduction of power and, hence, the size of the driving motor. A typical conventional stacked rotor includes a plurality of discs stacked in axial direction, with each disc being provided with a plurality of rotor blades fitted in dove-tail grooves formed in the outer peripheral surface thereof. The axially stacked discs are joined to form one body by stacking bolts received in axially aligned bolt holes formed in each of the discs. The bolt holes include reamer holes reamed with a high precision and clearance holes formed by drilling, with the reamer holes and the clearance holes being arranged in an alternating fashion. During assembling of the rotor problems are encountered due to errors arising during fabrication of the discs such as, for example, too small of a gap between the stacking bolts and reamer holes, and, for this purpose, the clearance holes are arranged alternatingly with the reamed holes. However,with a rotor having a small axial length, it is possible to ream all bolt holes to leave only a small clearance between the bolts and holes, because in such a case the overall length of the bolt holes is sufficiently small.
Thus, in the conventional stacked rotor, it is necessary to take a trouble of reaming bolt holes for the stacking bolts at an extremely high precision. Particularly, the assembling of the stacked rotor having a long axial length is quite difficult if all of the bolt holes are reamer holes.
In the conventional stacked rotor in which the reamer holes and the clearance holes are arranged alternatingly, a considerably large gap is formed between the stacking bolt and the wall of the clearance hole. Therefore, the stacking bolt is subjected to bending stresses and is deformed radially outwardly by centrifugal forces generated by rotation of the rotor. A large axial tensile stress is formed in the stacking bolt for tightly fastening the discs. Consequently, a large composite stress, composed of the bending stress and the tensile stress, is generated in each stacking bolt; therefore, the stacking bolts are subjected to a danger of rupture by fatigue.